TUESDAY, Sept. 24 (HealthDay News) -- Deadly bleeding in the brain, called a subarachnoid hemorrhage, can cause a crushing headache that sends people to the emergency room. Often, the condition is misdiagnosed, but Canadian researchers have developed a simple tool they say could help ER doctors make the right diagnosis.

Headache is a common complaint in the ER, accounting for about 2 percent to 4 percent of patient visits, said lead researcher Dr. Jeffrey Perry, an associate professor in the department of emergency medicine at the University of Ottawa.

"Most patients with headache just have a bad headache, which is not serious," Perry said. But 1 percent of these patients have a subarachnoid hemorrhage and it's missed in more than 5 percent of those cases, he noted.

If caught early, the condition is treatable. If it's not treated promptly, it can lead to disability or death.

"Physicians right now use their judgment to decide which patients they investigate to rule out subarachnoid hemorrhage," Perry said.

The researchers' approach may help doctors decide which patients need further tests, such as a CT scan, to definitively diagnose whether the patient has a subarachnoid hemorrhage or not.

Half of these patients have no neurological signs that would offer a clue to their condition. This is why this tool is useful, the study authors said.

According to the report, published in the Sept. 25 issue of the Journal of the American Medical Association, the key factors that warrant further examination are: headache starting during exertion; age; neck pain or stiffness; witnessed loss of consciousness, and a "thunderclap headache" with instantly peaking pain and limited neck movement, such as inability to raise the head three inches off the bed.

Perry and his team tested the tool, which they dubbed the Ottawa Subarachnoid Hemorrhage Rule, with 2,131 patients complaining of a headache that peaked within one hour and who had no neurological problems. Among these patients, 132 (6.2 percent) had a subarachnoid hemorrhage, the researchers found.

This test detected all the patients with a subarachnoid hemorrhage, but also falsely identified many others as having the condition, the researchers acknowledged.

Perry said he is working to improve the test to better exclude patients who don't have a subarachnoid hemorrhage.

One expert thinks the rule can be useful, but shouldn't be used to clear all patients with headaches.

"We would like not to miss subarachnoid hemorrhage," said Dr. David Newman-Toker, an associate professor of neurology at Johns Hopkins University School of Medicine in Baltimore and co-author of an accompanying journal editorial. "Having a more standardized way of approaching patients would be a good idea."

Newman-Toker, however, is concerned that by having a hard-and-fast rule for making a diagnosis, doctors are in danger of "turning their thinking caps off."

Sometimes they just go through the steps and pass the patient on, he said.

"There are a lot of other things that can cause bad headaches, and a lot of them are serious and this rule doesn't address those," he said. "So you have to be careful about extending the rule beyond the scope that it was designed for."